The idea of waning immunity has picked up steam in recent weeks, with some countries using it to justify rolling out third-dose COVID-19 vaccine boosters to their populations. But immunologists say the concept has been largely misunderstood.
While antibodies — proteins created after infection or vaccination that help prevent future invasions from the pathogen — do level off over time, experts say that's supposed to happen.
And it doesn't mean we're not protected against COVID-19.
"Waning has this connotation that something's wrong and there isn't," she said. "It's very normal for the immune system to mount a response where a ton of antibodies are made and lots of immune cells expand. And for the moment, that kind of takes over.
"But it has to contract, otherwise you wouldn't have room for subsequent immune responses."
Antibody levels ramp up in the "primary response" phase after vaccination or infection, "when your immune system is charged up and ready to attack," said
They then decrease from that "emergency phase," he added. But the memory of the pathogen and the body's ability to respond to it remains.
Kerfoot said B-cells, which make the antibodies, and T-cells, which limit the virus's ability to cause serious damage, continue to work together to stave off severe disease long after a vaccine is administered. While T-cells can't recognize the virus directly, they determine which cells are infected and kill them off quickly.
Recent studies have suggested the T-cell response is still robust several months following a COVID-19 vaccination.
"You might get a minor infection ... (but) all of those cells are still there, which is why we're still seeing very stable effectiveness when it comes to preventing severe disease," Kerfoot said.
A pre-print study released this week by
So the concept of waning immunity depends on whether you're measuring protection against infection or against severe disease, Kerfoot said.
"You'll hear people say that vaccines aren't designed to protect infection, they're designed to prevent severe disease," Kerfoot said. "I wouldn't say necessarily it's the vaccine that's designed to do one or another ... that's just how the immune system works."
Pfizer-BioNTech has argued the same with its own data, and an advisory panel to the
However, the panel rejected boosters for the general population, saying the pharmaceutical company had provided little safety data on extra jabs.
Gommerman said the efficacy data presented by
"The fact it protects 87 per cent against infection, that's incredible," she said. "Most vaccines can't achieve that."
Bancel said
But Dr.
"This idea of waning immunity is being exploited and it's really concerning to see," Chakrabarti said. "There's this idea that antibodies mean immunity, and that's true ... but the background level of immunity, the durable T-cell stuff, hasn't been stressed enough."
While some experts maintain boosters for the general population are premature, they agree some individuals would benefit from a third jab.
Other experts have argued residents of long-term care, who were prioritized when the rollout began last December, may also soon need a third dose. The English study suggests immunity could be waning in older groups but not much — if at all — among those under age 65.
Chakrabarti said a decrease in protection among older populations could be due more to "overlapping factors," including their generally weaker immune systems and congregate-living situations for those in long-term care.
"These are people at the highest risk of hospitalization," he said. "Could (the length of time that's passed following their doses) be playing a role? Yeah, maybe."
While we still don't know the duration of the immune response to COVID-19 vaccination, Gommerman said immune cells typically continue to live within bone marrow and make small amounts of antibodies for "decades."
"And they can be quickly mobilized if they encounter a pathogen," she said.
This report by
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